A pressure gauge consists in principle of a spring element (measuring element) is and a measuring or sensor organ. Common commercially available pressure gauges based on silicon technology may use membranes as the spring element, provided with piezo-resistive resistors as the sensor organs. Such membrane sensors have a typical size of 3 mm×4 mm. Spring elements like membranes are disadvantageous for high pressures because such elements are susceptible for effects related to restraining to a substrate with transition to materials with different modules of elasticity. The tension detected on such membranes will be a combination of pressure and tensile stresses. If the tensile stress becomes adequately high, breakage may occur. At large deformations, the stress in the membrane will not be linearly dependent of the pressure, providing a non-linear signal.
The closest prior art in this connection is described in Norwegian Patent NO 304 328 describing a pressure gauge particularly for very high pressures. The measuring principle that is used is described in the book “Instrumenteringsteknikk” by Ole A. Solheim, Tapir forlag Trondheim 1966, and uses piezo-resistive elements arranged on the outside of the measuring element for detecting tensile stress appearing in the measuring element. The two parts of the measuring element are manufactured with planar techniques, preferably of silicon or quartz, and have a considerably greater length than transverse dimension, with the cavity running in the longitudinal direction. The pressure gauge is, however, especially suitable for measuring very high pressures.
The present invention represents a further development of the sensor described in the Norwegian Patent NO 304 328 to lower pressure ranges.